There are two subdivisions of the nervous system. The first is the central nervous system which encompasses the brain and spinal cord. The second is the peripheral nervous system, including the nerves which arise from the central nervous system.
The autonomic system includes all the parts of the peripheral nervous system involved in normally unconscious actions such as the control of internal organs, glands, and all smooth muscles of the body. The autonomic system is further divided into parasympathetic and sympathetic nervous systems. These are said to be antagonistic systems.
The sympathetic system is involved in the "fight or flight" reflexes. It dilates the pupils of the eyes, increases heart rate, constricts blood vessels in the skin and stomach, and dilates blood vessels in the muscles. The parasympathetic system does the opposite. Among other things, it constricts pupils of the eyes, reduces heart rate, and stimulates secretion of the digestive juices.
Neurons of the peripheral nervous system can regenerate; neurons of the central nervous system cannot. If the spinal cord is severely damaged, paralysis can occur. This type of paralysis is determined by where the damage occurs.
Antony, C.P. & G.A. Thibodeaw. 1979. Textbook of Anatomy and Physiology. The C.V. Mosby Company, St. Louis. 731 pp.
Eckert, R. & D. Randall. 1983. Animal Physiology, second edition W. H. Freeman and Company, San Francisco. 830 pp.
Lockhart, R.D., G.F. Hamilton, et. al. 1974. Anatomy of The Human Body. Faber and Faber Limited. London. 697 pp.
Rahlman, J. & J.L. Smith. 1981. Ucla Kinesiology 14 Human Neuromuscular Anatomy. Academic Publishing Service. L A. 490 pp.
Van Amerongen, C. The Way Things Work; Book Of The Body. New York: Simon and Schuster, 1979.
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